1. Field of the Invention
This invention is in the field of extrusion apparatus and is particularly concerned with a novel smoothing and cooling means for contacting the material with air blasts immediately upon extrusion wherein air streams are applied from a number of different points in the die assembly to effectively provide air currents about the entire peripheries of the ribbons being extruded.
2. Description of the Prior Art
While the extrusion of thermoplastic resins is an old and highly developed art, the same is not true of the extrusion of granular inorganic materials utilizing a thermoplastic binder. Such compositions are used as fertilizer sticks and may include granular sources of nitrogen, phosphorus and potassium, combined with a binder of a water soluble, thermoplastic resin. When such materials are extruded, there is a tendency to trap vapor in the extrusion mass which, upon leaving an extrusion orifice, tends to expand due to the very substantial reduction in pressure, pushing granular particles to the periphery and creating a very rough surface on the exudate. The desired homogeniety is thus reduced, and an undesirably coarse surface is obtained.